Therapeutic compounds may be administered by a variety of routes, depending on the nature of the drug, the pharmacokinetic profile desired, patient convenience, and cost, among other factors. Among the most common routes of drug delivery are oral, intravenous (IV), intramuscular (IM) intraperitoneal (IP) subcutaneous, transdermal, transmucosal, and by inhalation to the patient's respiratory tract.
The inhalation route of drug administration offers several advantages for certain drugs, and in treating certain conditions. Since the drug administered passes quickly from the respiratory tract to the bloodstream, the drug may be active within a few minutes of delivery. This rapid drug effect is clearly advantageous for conditions like asthma, anaphylaxis, pain, and so forth where immediate relief is desired.
Further, the drug is more efficiently utilized by the patient, since the drug is taken up into the bloodstream without a first pass through the liver as is the case for oral drug delivery. Accordingly, the therapeutic dose of a drug administered by inhalation can be substantially less, e.g., one half that required for oral dosing.
Finally, since inhalation delivery is convenient, patient compliance can be expected to be high.
As is known, efficient aerosol delivery to the lungs requires that the particles have certain penetration and settling or diffusional characteristics. For larger particles, deposition in the deep lungs occurs by gravitational settling and requires particles to have an effective settling size, defined as mass median aerodynamic diameter (MMAD), of between 1-3.5 μm. For smaller particles, deposition to the deep lung occurs by a diffusional process that requires having a particle size in the 10-100 nm, typically 20-100 nm range. Particle sizes that fall in the range between 10-100 nm and 1-3.5 μm tend to have poor penetration and poor deposition. Therefore, an inhalation drug-delivery device for deep lung delivery should produce an aerosol having particles in one of these two size ranges.
Another important feature of an aerosol delivery device is control over total dose delivered, that is, the amount of aerosol generated should be predictable and repeatable from one dosing to another.
Other desirable features for an inhalation device are good product storageability, without significant loss of drug activity.
It would therefore be desirable to provide an aerosol inhalation device that provides these features in a simple, easily operated inhalation device.